Measure your space in square feet, then multiply by the depth you want

The amount of mulch you need depends on two things: the area you are covering and how deep you want the layer to be. Most landscaping jobs use mulch between 2 and 4 inches deep. To find how much to buy, measure the length and width of each bed in feet, multiply those numbers together to get square feet, then use a straightforward formula based on your chosen depth.

The math is straightforward. For a 2-inch depth, divide your total square feet by 162. For 3 inches, divide by 108. For 4 inches, divide by 81. The result is how many cubic yards of mulch to order. If your space is irregular or has curves, break it into rectangles, calculate each one, and add them together.

Most mulch is sold by the cubic yard, though some suppliers sell by the bag. A cubic yard covers about 162 square feet at 2 inches deep, 108 square feet at 3 inches, or 81 square feet at 4 inches. Knowing this lets you work backward from the depth you want to the amount you need to buy.

Key Takeaways

  • Measure the length and width of each bed in feet, multiply them together, then use the depth formula: divide by 162 for 2 inches, 108 for 3 inches, or 81 for 4 inches.
  • A cubic yard of mulch covers roughly 162 square feet at 2 inches deep, which is the standard depth for most garden beds.
  • Break irregular or curved beds into rectangles, calculate each section separately, and add the totals together.
  • Add 10 to 15 percent extra to your total to account for settling and uneven ground, especially if you are working with existing mulch.

How to measure a rectangular bed

Start with a straightforward rectangle. Measure the length in feet from one end to the other. Then measure the width in feet from side to side. Multiply length times width. That number is your square footage.

For example, a bed that is 10 feet long and 4 feet wide is 40 square feet. If you want it 3 inches deep, divide 40 by 108. The answer is 0.37 cubic yards. Since suppliers usually sell whole or half yards, you would round up and order a half yard for that one bed.

How to handle irregular or curved beds

Curved beds and odd shapes are easier than they look. Imagine the bed as a series of overlapping rectangles, then calculate each rectangle separately. A kidney-shaped bed might break into a large rectangle in the middle and two smaller rectangles on the curved ends. Calculate all three, add them together, and you have your total.

If a bed has one curved side, you can approximate it by treating the curve as a triangle or trapezoid. Measure the straight sides and the depth of the curve, then use basic geometry. For a triangle, multiply base times height and divide by 2. For a trapezoid, add the two parallel sides, divide by 2, then multiply by the height. These rough estimates are close enough for mulch ordering.

Account for settling and uneven ground

Mulch settles over time as it breaks down and compacts. It also sits unevenly on ground that slopes or has dips. Most landscapers add 10 to 15 percent extra to their total to make up for this. If your calculation comes to 5 cubic yards, order 5.5 to 6 cubic yards instead.

Uneven ground matters more than you might think. If your bed slopes or has low spots, mulch will pool in the low areas and thin out on the high spots. Leveling the bed before you mulch saves you from having to add more later, but if you cannot level it, the extra 10 to 15 percent cushion becomes more important.

Depth matters for weed control and moisture

The depth you choose affects how well mulch does its job. A 2-inch layer is the minimum for light weed suppression and moisture retention. Three inches is the standard for most garden beds because it blocks most weeds while still letting water and air reach the soil. Four inches or deeper can work for heavy-traffic areas or very weedy spots, but it can also smother shallow-rooted plants and trap too much moisture in wet climates.

Do not go deeper than 4 inches unless you have a specific reason. Thick mulch can create a barrier that keeps water from reaching plant roots, and it can cause rot if it piles against the stems of shrubs or trees. Keep mulch a few inches away from tree trunks and plant bases for this reason.

Mulch sold by the bag versus by the yard

Bagged mulch is convenient for small beds but costs more per cubic yard than bulk mulch. A typical bag holds 2 to 3 cubic feet. Since a cubic yard is 27 cubic feet, you need 9 to 13 bags to make one cubic yard, depending on bag size. If you are covering more than 100 square feet, bulk mulch from a landscape supplier is usually cheaper and requires less hauling.

For small projects under 50 square feet, bags make sense. For anything larger, call a local mulch supplier, give them your square footage and desired depth, and ask for a quote on bulk delivery. Many suppliers deliver for free on orders over a certain amount, which can offset the delivery fee for larger jobs.

Common mistakes when ordering mulch

The biggest mistake is underestimating how much space you are covering. People often measure only the visible bed and forget about the edges or the area around trees. Measure twice, especially if you are ordering bulk mulch and cannot easily return the extra.

Another common error is choosing a depth that is too shallow. Two inches looks thinner than you expect once it is spread, and it settles to almost nothing within a few months. Three inches is the safer choice for most situations. Also, do not assume all mulch is the same. Shredded bark, wood chips, and dyed mulch all have different weights and coverage rates, though the cubic yard measurement stays the same.

Frequently Asked Questions

How many bags of mulch do I need for 100 square feet?

For 100 square feet at 3 inches deep, you need about 0.93 cubic yards. That is roughly 9 to 12 bags, depending on whether each bag is 2 or 3 cubic feet. Check the bag label for the exact volume, then divide your total cubic yards by that number.

Should I remove old mulch before adding new mulch?

You do not have to remove all of it, but you should rake out the top layer if it has become matted or compacted. Spread new mulch over the old layer, but do not pile it deeper than 4 inches total. If old mulch is still in good condition, adding 1 to 2 inches of fresh mulch on top is usually enough.

What if my bed is circular?

Measure the distance across the circle (the diameter) in feet. Multiply that number by itself, then multiply by 0.785. That gives you the square footage. For example, a circle with a 10-foot diameter is 78.5 square feet. Then use the depth formula as you would for any other shape.

Can I order mulch in cubic feet instead of cubic yards?

Yes, but most landscape suppliers sell by the cubic yard. If you find a supplier who sells by the cubic foot, divide your cubic yard total by 27 to convert. For example, 2 cubic yards equals 54 cubic feet. Bagged mulch is usually labeled in cubic feet, so check the bag before you buy.

How do I know if I ordered too much mulch?

Extra mulch can be stored in a dry place for next season, used in other beds, or given away. It does not go bad if kept dry, so having a little extra is better than running short and having to make another trip to the supplier.